Head-up display device with curved optical surface having total reflection

ABSTRACT

A display device for displaying information is provided with an optical system for guiding the light of the display device to the eye, the optical system having, in the order in the proceeding direction of the light, an entrance face for receiving the light, a curved face for totally reflecting the light and a reflecting face concave to the eye side and adapted to reflect the light toward the eye. The reflected light is transmitted by the curved face and reaches the eye. Thus there is obtained a compact display device with satisfactorily suppressed aberrations.

This application is a division of application Ser. No. 08/959,285 filedOct. 24, 1997, which is a continuation of application Ser. No.08/478,688 filed Jun. 7, 1995, now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an observation optical system, and moreparticularly to an optical system adapted for use in a device calledhead-up display or spectacle-type display.

2. Related Background Art

Conventionally there have been proposed display devices in which acathode ray tube (CRT) or a liquid crystal display (LCD) is positionedclose to the head of the observer whereby the observer is enabled toobserve the image formed by such CRT or LCD, as disclosed for example inU.S. Pat. Nos. 4,081,209 and 4,969,724 and Japanese Patent Laid-OpenApplication Nos. 58-78116, 2-297516 and 3-101709. Japanese PatentLaid-Open Application No. 3-101709 discloses an observation deviceproviding a relatively easily observable real image by re-focusing anoriginal image. However, a considerably large space is unavoidablebecause an optical lens is employed for re-imaging.

On the other hand, U.S. Pat. Nos. 4,081,209 and 4,969,724 and JapanesePatent Laid-Open Application Nos. 58-78116 and 2-297516 discloseobservation devices designed to observe a false image which isadvantageous for compactizing the device though it is somewhat inferiorin the ease of observation.

Though the observation device of the latter type can achievecompactization in comparison with that of the real image type, theextent of such compactization cannot be said sufficient. Among theabove-mentioned prior technologies, the one disclosed in the JapanesePatent Laid-Open Application No. 58-78116 is relatively advanced interms of compactization, but the device still has a large thickness inthe direction of the axis of the eye. It is also described that theobserved image involves optical distortion, astigmatism and coma. Arelated technology is also described in U.S. patent application Ser. No.08/317,528 filed Oct. 4, 1994.

SUMMARY OF THE INVENTION

In consideration of the foregoing, an object of the present invention isto provide a compact and thin observation optical system.

Another object of the present invention is to provide an observationoptical system with reduced aberrations.

The above-mentioned objects can be attained, according to an aspect ofthe present invention, by a display device comprising display means fordisplaying information, and optical means provided with curved faces forguiding the light from said display means to the eye, wherein saidoptical means has, in succession in the proceeding direction of the eye,a light entrance face for introducing the light, a curved face fortotally reflecting the light and a face concave to the eye forreflecting the light toward the eye whereby the light reaches the eye byway of these curved faces and a compact display device can be attainedwith satisfactorily suppressed aberrations.

Still another object of the present invention is to provide theabove-mentioned display device with a visual axis detecting devicethereby controlling the display state of said display means.

Still other objects of the present invention, and the features thereof,will become fully apparent from the following description of theembodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are views showing optical paths in the observationoptical system of the present invention;

FIGS. 2A and 2B are views showing a cross section and optical paths inthe observation optical system of a numerical example 1 of the presentinvention;

FIGS. 3A and 3B are views showing a cross section and optical paths inthe observation optical system of a numerical example 2 of the presentinvention;

FIGS. 4A and 4B are views showing a cross section and optical paths inthe observation optical system of a numerical example 3 of the presentinvention;

FIGS. 5A and 5B are views showing a cross section and optical paths inthe observation optical system of a numerical example 4 of the presentinvention;

FIGS. 6 and 7 are optical cross-sectional views showing the basicprinciple of the observation optical system of the present invention;

FIGS. 8A and 8B are schematic views showing the optical paths of anobservation optical system of the present invention;

FIG. 9 is a schematic view showing the optical path of a visual axisdetecting system employed in the present invention;

FIGS. 10 and 11 are schematic views showing states when the displaydevice of the present invention is worn by the observer;

FIGS. 12A and 12B are partial magnified views of FIGS. 8A and 8B;

FIG. 13 is a partial schematic view in the vicinity of a prism member inan embodiment 6 of the present invention;

FIG. 14 is a partial schematic view in the vicinity of a prism member inan embodiment 7 of the present invention;

FIG. 15 is a partial schematic view in the vicinity of a prism member inan embodiment 8 of the present invention;

FIG. 16 is a partial schematic view in the vicinity of a prism member inan embodiment 9 of the present invention;

FIGS. 17A and 17B are schematic views showing the optical paths of anobservation system and a visual axis detecting system in an embodiment 8of the present invention;

FIGS. 18A and 18B are schematic views showing the optical paths of anobservation system and a visual axis detecting system in an embodiment 9of the present invention;

FIGS. 19A and 19B are partial schematic views of an observation opticalsystem and a visual axis detecting optical system, respectively, of thepresent invention;

FIG. 20 is a flow chart showing the control sequence of the presentinvention;

FIG. 21 is a schematic view showing selectable display areas in thepresent invention;

FIG. 22 is a schematic view showing points for display area selection inthe present invention;

FIGS. 23A and 23B are partial schematic views of an observation opticalsystem and a visual axis detecting optical system, respectively, of thepresent invention; and

FIG. 24 is a flow chart showing the control sequence of the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

At first there will be explained the basic principle of the displayoptical system of the present invention, with reference to FIGS. 1A, 1Band 6. Display means 4, for displaying an original image such as acharacter or a pattern, is composed for example of a known liquidcrystal display (LCD) device. There are also provided a first opticalmember 3 a for guiding the light from the display means 4 to the eye ofthe observer, and a second optical member 3 b. The light from thedisplay means 4 at first enters the first optical member 3 a, then istotally reflected by a totally reflecting face 1, at the eye side, ofthe first optical member, further reflected by a concave half mirror 2,concave to the eye of the observer, transmitted by the above-mentionedtotally reflecting face 1 and guided to the eye.

FIGS. 1A and 1B illustrate the optical path, seen respectively from thetop and from the side.

As the concave mirror 2 is composed of a half mirror, the observer canobserve the image on the display means 4, superimposed with the externalscenery. Although the present embodiment provides a superimposingdevice, there may also be provided a device for merely observing theimage display, in which case the concave mirror is composed of a mirror.

Owing to the above-explained configuration, the present and ensuingembodiments provide extremely thin, compact display devices, with athickness of the optical system in the order of 10 to 15 mm. Also thereis achieved a wide viewing angle of ca. ±16.80 in the horizontaldirection and ca. ±11.40 in the vertical direction.

Such compactization, wide viewing angle and satisfactory opticalperformance are derived in the present embodiment from fact that a faceat the observer side is utilized as a totally reflecting face and atransmitting face, and that the concave mirror 2 is positionedconsiderably eccentric with respect to the optical axis of the eye. Inaddition there are significant contributions from facts that the totallyreflecting face is constituted by a curved surface, particularly withoptical power variable depending on the azimuthal angle as will be shownin the following numerical examples, and that the concave mirror 2 isgiven an optical power depending on the azimuthal angle.

In particular, the optical power depending on the azimuthal angle, givento the concave mirror 2, allows to sufficiently eliminate the eccentricaberration resulting from the eccentric positioning thereof. Also thetotally reflecting face is similarly constituted by a curved surface tocorrect the aberrations generated by the concave mirror.

In the following description, the folding direction of the light will becalled the direction of generatrix, while a direction perpendicularthereto will be called the direction of meridian. In the presentembodiment, the image angle is made wider in the meridian direction, anda relatively strong positive refractive power of the concave mirrorgenerates aberrations, but the totally reflecting face is given, in thecross section along the meridian direction, a negative optical power tocorrect such aberrations. Along the optical path in the cross section inthe meridian direction from the side of the display device or the sideof the eye of the observer, there are provided, in succession of a faceof a negative refractive power, a face of a positive refractive power(concave mirror) and a face of a negative refractive power, so that theaberrations are easy to eliminate because of such symmetricalarrangement of the refractive powers.

For reducing the thickness in the direction of optical axis of the eye,the elements are desirably so arranged that the optical system 3 standsupright. More specifically, referring to FIG. 7, there is preferablysatisfied a condition:|α|≦20°wherein α is the angle (tilt angle) of the tangential line to thetotally reflecting face 1 at the vertex thereof, to a line perpendicularto the optical axis of the eye. Outside this range, the optical systembecomes thicker in the direction of the optical axis, whereby the devicebecomes bulkier. Also in case of superimposing an image on the scenery,the inclination of the optical member becomes larger to cause adistortion in the observed scenery.

More preferably there is satisfied a condition:−15°≦α≦5°Below the lower limit, the optical system can be made thinner in adirection parallel to the optical axis of the eye, but the distortionbecomes severer. Above the upper limit, the optical system becomesthicker in a direction parallel to the optical axis of the eye, and theprisms become undesirably heavy.

In the present embodiment, since the totally reflecting face is concaveto the eye, the light entrance face at the outside is constituted by asubstantially same curved surface in order to prevent the distortion inthe observed scenery.

The concave mirror 2 is made considerably eccentric with respect to theoptical axis of the eye, whereby an eccentric aberration is generated.However this eccentric aberration is satisfactorily corrected byconstituting the totally reflecting face with a curved surface andemploying, in the concave mirror 2, a surface of which curvature variesdepending on the azimuthal angle (toric or anamorphic surface).Preferably an aspherical surface (toric aspherical or anamorphicaspherical surface) to attain an extremely satisfactory opticalperformance.

With respect to the generatrix direction (y-direction) which is thedirection of folding of the light and the meridian directionperpendicular thereto, the faces of the optical system are so designedto have optical powers variable depending on the azimuthal angle, but,in the entire system, the paraxial focal length is preferablysubstantially constant in any direction. More specifically, there ispreferably satisfied a condition:0.9<|f _(y) /f _(x)|<1.1wherein f_(y) and f_(x) are paraxial focal lengths of the entire systemrespectively along the cross section in the direction of generatrix andthat in the direction of meridian.

Also the totally reflecting face (or transmitting face) or the concavemirror is so designed, as explained in the foregoing, as to vary theoptical power depending on the azimuthal angle thereby suppressing theeccentric aberration, and, for this purpose, there is preferablysatisfied a condition:|r_(x)|<|r_(y)|wherein r_(y) and r_(x) are radii of paraxial curvature of said facerespectively in the cross section in the generatrix direction and inthat in the meridian direction.

In the present embodiment, for achieving compact configuration, theconcave mirror 2 is significantly tilted (decentralized) in thedirection of generatrix which is the direction of folding of the light,the eccentric aberration is generated larger in the direction ofgeneratrix than in the direction of meridian. Thus the optical power inthe cross section in the direction of generatrix is made weaker thanthat in the cross section in the direction of meridian, namely theradius of paraxial curvature is made longer in the direction ofgeneratrix as indicated in the foregoing condition, thereby suppressingthe eccentric aberration in the direction of generatrix.

Preferably these curvatures are so selected as to satisfy:|r _(x) /r _(y)<0.85

Outside this range, the eccentric aberration becomes conspicuouslylarge.

On the other hand, in case the entrance face 5 is so constructed as tohave varying optical power depending on the azimuthal angle as in thefollowing numerical examples 2 to 4, the eccentric aberration can besuppressed by inversely satisfying a condition:|r_(x)|>|r_(y)|

For further satisfactory correction of aberrations, there are preferablysatisfied conditions:−2.0<2f _(x) /r _(x2)<−0.1  (a)−2.5<2f _(x) /r _(x3)<−0.5  (b)wherein r_(x2) and r_(x3) are radii of paraxial curvature respectivelyof the totally reflecting face (or transmitting face) 1 and the concavemirror 2, in the cross section in the meridian direction.

Below the lower limit of the condition (a), the curvature (negativepower) of the totally reflecting face in the meridian direction becomesstronger and the correction of distortion becomes difficult. Also belowthe lower limit of the condition (b), the curvature (positive power) ofthe concave mirror in the meridian direction becomes strong and thecorrection of astigmatism becomes difficult. On the other hand, abovethe upper limit of the condition (a), the curvature of the totallyreflecting face in the meridian direction comes to have a positivepower, so that the totally reflecting condition becomes difficult tosatisfy. Also above the upper limit of the condition (b), the positivepower of the concave mirror in the meridian direction becomes weaker, sothat the thickness of the optical system in a direction parallel to theoptical axis of the eye becomes undesirably large.

Furthermore, there are preferably satisfied conditions:−1.0<2f _(y) /r _(y2)<0  (c)−2.5<2f _(y) /r _(y3)<−0.2  (d)wherein f_(y) is the focal length of the entire system in the generatrixdirection, r_(y2) is the radius of curvature of the totally reflectingface, and r_(y3) is the radius of curvature of the concave mirror.

Below the lower limit of the condition (c), the negative power of thetotally reflecting face in the generatrix direction becomes stronger, sothat the eccentric distortion becomes difficult to correct. Below thelower limit of the condition (d), the positive power of the concavemirror in the generatrix direction becomes stronger, thereby generatinga large eccentric astigmatism. Also above the upper limit of thecondition (c) relating to the totally reflecting condition in thegeneratrix direction, it becomes difficult to satisfy the totallyreflecting condition. Also above the upper limit of the condition (d)relating to the power of the concave mirror in the generatrix direction,this power becomes weaker so that the entire length of the opticalsystem extends in the generatrix direction.

In the foregoing, the structures of the totally reflecting face (ortransmitting face) 1 and the concave mirror 2 have been explained inrelation principally with the curvature, but, in the present embodiment,the concave mirror 2 is subjected to a parallel shift, in the directionof generatrix (y-direction), from the optical axis of the eye toward theoriginal image side (+) as shown in FIG. 7, whereby the eccentricdistortion in the generatrix direction can also be suppressed.

The eccentric distortion can be suppressed by a parallel shiftsatisfying:E≧2.5 mmwherein E is the amount of the parallel shift or the distance from theoptical axis of the eye to the vertex of the concave mirror surface inthe direction of generatrix (cf. FIG. 7). In the following example 1,this amount E of parallel shift is equal to 5.2 mm, but it may beselected larger as in other examples for satisfactorily correcting theaberrations, and preferably satisfied a condition E≧23 mm.

Then, with respect to the entrance face 5, the angle θβ between theentrance face and the original image surface constituting the displaymeans, in the direction of generatrix, is preferably so selected as tosatisfy a condition:5°≦θβ≦30°Below the lower limit, the entrance face and the original image surfacebecome closer to parallel, so that the original image becomesundesirably thick in the direction parallel to the optical axis of theeye. On the other hand, above the upper limit, the original imagebecomes perpendicular to the direction parallel to the optical axis ofthe eye.

The present embodiment assumes, though not illustrated, the use of arear light source or direct natural light for illuminating the originalimage. If the original image becomes perpendicular to theabove-mentioned optical axis, it becomes difficult to efficiently obtainnatural light for direction illumination and the false image obtained bythe reflective optical system becomes darker. Consequently the presentembodiment utilizes the natural light illumination and the back lightillumination selectively by detecting the external illuminationintensity, thereby utilizing the natural light illumination in thedaytime when the natural light is strong and the back light illuminationat night.

The display means 4 for forming the original image is composed of aliquid crystal display (LCD) device for compactizing the entire device,and the angle γ between the optical axis at the center of the originalimage and the principal ray of the light emerging from the originalimage (central light beam of the diaphragm constituted by the eye) (cf.FIG. 7) is preferably so selected as to satisfy:|γ|≦10°This condition is required in case a liquid crystal display device isemployed for providing the original image. The liquid crystal display ingeneral has a narrow viewing angle, the light obliquely entering thedisplay device and emerging therefrom is easily lost. Therefore, abright false image cannot be obtained unless the light is made to enterthe liquid crystal display surface and to emerge therefrom asperpendicularly as possible. The above-mentioned condition allows toobserve a sufficiently bright image.

FIGS. 2A to 5B are optical cross-sectional views respectively ofnumerical examples 1, 2, 3, and 4 explained in the following. Theconfiguration shown in FIGS. 2A and 2B employs toric aspherical surfacesin the concave mirror and

the totally reflecting face. The configuration shown in FIGS. 3A and 3Bemploys anamorphic aspherical surfaces in each of the concave mirror,totally reflecting face and light entrance face. Also the configurationsshown in FIGS. 4A to 5B employ anamorphic aspherical surfaces in all theoptical faces.

In the numerical examples 2 to 4 corresponding to FIGS. 3A to 5B, theentrance face 5 is also provided with a curvature for attaining moresatisfactory correction of aberrations.

In the present embodiment, all the optical members are composed ofacrylic resin, but glass may naturally be employed instead.

In the following there are shown numerical examples of the presentembodiment, wherein TAL indicates a toric aspherical lens face, and AALindicates an anamorphic aspherical lens face.

The TAL is defined by:

$z = {\frac{y^{2}/r_{yi}}{1 + \sqrt{1 - {\left( {1 + k_{i}} \right)\left( {y/r_{yi}} \right)^{2}}}} + {A_{i}y^{4}} + {B_{i}y^{6}} + {C_{i}y^{8}} + {D_{i}y^{10}}}$wherein i indicates the face number.

Also the AAL is defined by:

$z = {\frac{{y^{2}/r_{yi}} + {x^{2}/r_{xi}}}{1 + \sqrt{1 - \left\lbrack {{\left( {1 + k_{yi}} \right)\left( {y/r_{yi}} \right)^{2}} + {\left( {1 + k_{xi}} \right)\left( {x/r_{xi}} \right)^{2}}} \right\rbrack}} + {{AR}_{i}\left\{ {{\left( {1 + {AP}_{i}} \right)y^{2}} + {\left( {1 - {AP}_{i}} \right)x^{2}}} \right\}^{2}} + {{BR}_{i}\left\{ {{\left( {1 + {BP}_{i}} \right)y^{2}} + {\left( {1 - {BP}_{i}} \right)x^{2}}} \right\}^{8}} + {{CR}_{i}\left\{ {{\left( {1 + {CP}_{i}} \right)y^{2}} + {\left( {CP}_{i} \right)x^{2}}} \right\}^{4}} + {{DR}_{i}\left\{ {{\left( {1 + {DP}_{i}} \right)y^{2}} + {\left( {1 - {DP}_{i}} \right)x^{2}}} \right\}^{8}}}$wherein i indicates the face number.

A_(i) and B_(i) are aspherical coefficients.

In the following examples, at least the totally reflecting face isconstructed with a face with variable refractive power depending on theazimuthal angle, but it may also be constructed with a rotationallysymmetrical spherical or aspherical face.

EXAMPLE 1

r_(yi)[mm] r_(xi)[mm] radius of radius of curvature in curvature in y, ztilt angle in generatrix meridian coordinates generatrix directiondirection of vertex direction i = 1 ∞ (0, 0) 0 2 −548.019 −74.077(−0.05, 19.80) T A L 0 3 −57.595 −40.526 (5.10, 29.14) T A L 22 in 4−548.019 −74.077 (−0.05, 19.80) T A L 0 {close oversize brace} prism 5 ∞(18.58, 28.07) 68.90 6 ∞ (21.38, 29.15) 51.17 K₂,K₄ A₂,A₄ B₂,B₄ C₂,C₄D₂,D₄ (TAL2,4) 613.869 −0.473E−5 0.326E−7 −0.940E−10 0.991E−13 K₃ A₃ B₃C₃ D₃ (TAL3) −1.360 0.345E−5 −0.301E−7 0.944E−10 −0.113E−12 refractiveindex 1.49171 focal length in f_(y) = 21.07 mm (d-line) of prismgeneratrix direction Abbe's number 57.4 focal length in f_(x) = 21.86 mm(d-line) of prism meridian direction (numerical data) α = 1.8° E = 5.2mm |f_(y)/f_(x)| = 0.96 γ = 1.36 |r_(x)/r_(y)| = 0.7 β = 17.72f_(x)/r_(xi) = −0.59 2f_(x)/r_(xi) = −1.08 2f_(y)/r_(yi) = −0.082f_(y)/r_(yi) = 0.73

EXAMPLE 2

r_(yi)[mm] r_(xi)[mm] radius of radius of curvature in curvature in y, ztilt angle in generatrix meridian coordinates generatrix directiondirection of vertex direction i = 1 ∞ (0, 0) 0 2 −2158.074 −32.224(0.60, 19.83) A A L −10.55 3 −63.157 −32.870 (34.76, 30.90) A A L 15.81in 4 −2158.074 −32.224 (0.60, 19.83) A A L −10.55 {close oversize brace}prism 5 72.108 1049.744 (14.82, 29.00) A A L 53.74 6 ∞ (17.03, 30.62)42.91 (AAL2,4) K_(y2,4) K_(x2,4) AR_(2,4) BR_(2,4) CR_(2,4) DR_(2,4)−13763.5 −3.896 −0.170E−4 0.401E−7 −0.154E−9 0.223E−12 AP_(2,4) BP_(2,4)CP_(2,4) DP_(2,4) −0.245 0.416E−1 0.870E−1 0.203E−1 (AAL3) K_(y3) K_(x3)AR₃ BR₃ CR₃ DR₃ 1.238 0.279 −0.317E−5 0.248E−8 −0.179E−11 0.608E−15 AP₃BP₃ CP₃ DP₃ 0.249 0.327E−2 −0.192E−1 0.181E−1 (AAL5) K_(y5) K_(x5) AR₅BR₅ CR₅ DR₅ 6.285 −1.33E−6 −0.114E−4 −0.402E−6 0.113E−8 −0.411E−10 AP₅BP₅ CP₅ DP₅ 0.273E1 0.155E1 0.160E1 −0.644 refractive index 1.49171focal length in f_(y) = 23.20 mm (d-line) of prism generatrix directionAbbe's number 57.4 focal length in f_(x) = 24.09 mm (d-line) of prismmeridian direction (numerical data) α = −10.5° 2f_(x)/r_(xi) = −1.52f_(y)/r_(yi) = −0.73 |f_(y)/f_(x)| = 0.96 2f_(x)/r_(xi) = −1.47 E =34.1 mm r_(x)|/r_(y) = 0.52 2f_(y)/r_(yi) = −0.02 γ = 0.23° β = 10.8°

EXAMPLE 3

r_(yi)[mm] r_(xi)[mm] radius of radius of curvature in curvature in y, ztilt angle in generatrix meridian coordinates generatrix directiondirection of vertex direction i = 1 ∞ (0, 0) 0 2 −3945.723 −49.792(3.665, 20.415) A A L 0.04 3 −67.136 −38.803 (36.403, 32.01) A A L 14.60in 4 −3945.723 −49.792 (3.665, 20.415) A A L 0.04 {close oversize brace}prism 5 123.302 843.030 (19.610, 28.357) A A L 61.72 6 ∞ (22.402,29.859) 52.54 (AAL2,4) K_(y2,4) K_(x2,4) AR_(2,4) BR_(2,4) CR_(2,4)DR_(2,4) 7202.73 −7.709 −0.142E−7 0.379E−7 −0.154E−9 0.198E−12 AP_(2,4)BP_(2,4) CP_(2,4) DP_(2,4) −0.183 0.710E−1 0.514E−1 0.201E−1 (AAL3)K_(y3) K_(x3) AR₃ BR₃ CR₃ DR₃ 1.066 0.193 −0.222E−5 0.321E−8 −0.188E−110.461E−15 AP₃ BP₃ CP₃ DP₃ 0.390 0.586E−1 −0.185E−1 −0.222E−1 (AAL5)K_(y5) K_(x5) AR₅ BR₅ CR₅ DR₅ −85.544 −916252 −0.913E−6 −0.204E−90.117E−13 −0.227E−10 AP₅ BP₅ CP₅ DP₅ 0.989E1 0.128E1 0.128E2 −0.952E−1refractive index 1.49171 focal length in f_(y) = 23.71 mm (d-line) ofprism generatrix direction Abbe's number 57.4 focal length in f_(x) =23.70 mm (d-line) of prism meridian direction (numerical data) α =−0.05° 2f_(x)/r_(xi) = −0.95 2f_(y)/r_(yi) = −0.71 |f_(y)/f_(x)| = 1.02f_(x)/r_(xi) = −1.22 E = 25.6 mm |r_(x)/r_(y)| = 0.58 2f_(y)/r_(yi) =−0.01 γ = 1.97° β = 15.5°

EXAMPLE 4

r_(yi)[mm] r_(xi)[mm] radius of radius of curvature in curvature in y, ztilt angle in generatrix meridian coordinates generatrix directiondirection of vertex direction i = 1 ∞ (0, 0) 0 2 −3752.581 −50.580(2.85, 23.13) A A L 0 3 −66.938 −38.651 (36.37, 34.72) A A L 14.15 in 4−3752.581 −50.580 (2.85, 23.13) A A L 0 {close oversize brace} prism 5306.125 1095.447 (18.59, 31.48) A A L 69.84 6 ∞ (21.46, 32.54) 51.20(AAL2,4) K_(y2,4) K_(x2,4) AR_(2,4) BR_(2,4) CR_(2,4) DR_(2,4) −33820.5−11.350 −0.144E−4 0.398E−7 −0.153E−9 0.201E−12 AP_(2,4) BP_(2,4)CP_(2,4) DP_(2,4) −0.152 0.730E−1 0.494E−1 0.255E−1 (AAL3) K_(y3) K_(x3)AR₃ BR₃ CR₃ DR₃ 1.063 0.127 −0.225E−5 0.316E−8 −0.188E−11 0.474E−15 AP₃BP₃ CP₃ DP₃ 0.372 0.568E−1 −0.168E−1 −0.208E−1 (AAL5) K_(y5) K_(x5) AR₅BR₅ CR₅ DR₅ 745.334 −651374 −0.656E−6 0.124E−6 0.474E−12 −0.972E−11 AP₅BP₅ CP₅ DP₅ 0.837E1 −0.273 0.563E1 −0.538 refractive index 1.49171 focallength in f_(y) = 23.09 mm (d-line) of prism generatrix direction Abbe'snumber 57.4 focal length in f_(x) = 23.09 mm (d-line) of prism meridiandirection (numerical data) α = 0° 2f_(x)/r_(xi) = −0.91 2f_(y)/r_(yi) =−0.69 |f_(y)/f_(x)| = 1.0 2f_(x)/r_(xi) = −1.19 E = 33.5 mm|r_(x)/r_(y)| = 0.58 2f_(y)/r_(yi) = −0.01 γ = 1.52° β = 18.6°

As explained in the foregoing, the present invention provides aspectacle-type display having a wide viewing angle of ±16.8° in thehorizontal direction and ±11.4° in the vertical direction, and anextremely small thickness of 10 to 15 mm in the direction parallel tothe optical axis of the eye. It also provides satisfactorily brightoptical performance. Furthermore, by constituting the concave mirrorwith a half-transmitting face, it is rendered possible to superimpose abright false image of the original image with the scenery withoutdistortion.

The foregoing embodiment has been designed to obtain a wide viewingangle, but the thickness may be made even smaller if a somewhat narrowerviewing angle is selected, since the thickness according to the presentinvention is variable depending on the viewing angle.

In the following embodiment, there has principally been explained theoptical system relating to the display of a head-up display device. Inthe following there will be explained a device based on theabove-explained optical system and provided further with visual linedetecting function.

FIGS. 8A and 8B are partial cross-sectional views showing the opticalpath of an observation system and a visual line detecting system in anembodiment of the present invention, while FIG. 9 is a partial plan viewof the systems shown in FIGS. 8A and 8B, and FIGS. 10 and 11 areschematic views showing the mode of use when the device of the presentinvention is mounted on the head of the observer.

In these drawings, there are shown an observer 101, display means 4composed for example of a liquid crystal display device and serving todisplay image information in the visible wavelength region, based onsignals from image information supply means such as a CD-ROM 105 or avideo camera 106, and an optical member 10 consisting of a transparentparallel-faced flat plate and incorporating therein a dichroic mirror 7serving as a beam splitter for transmitting the visible light andreflecting the infrared light. The dichroic mirror 7 may however bereplaced by a simple half mirror.

A prism member 3 is provided with a front face 1 consisting of a toricaspherical surface and effecting total reflection in a part; a rear face6 consisting of a transparent or opaque, flat or curved surface; aconcave face 2 consisting of a semi-transmitting or mirror-reflectingtoric aspherical surface provided in the prism member 3; and an entranceface 5. An optical axis (central axis) 104 coincides with the opticalaxis of the eye 103. The elements in the optical path from the displaymeans 4 to the eye 103 constitute an observation system, for observing afalse image of the image information displayed on the display means 4.Light source means 102 projects infrared light (wavelength of about 880nm) to the eye 103 so as to form Purkinje's images, in order to detectthe visual line of the eye 103 of the observer 101.

When the infrared light from the light source means 102 is projectedonto the eye 103 of the observer 101 as shown in FIG. 8B, an imagingoptical system (imaging lens) 8 forms a corneal reflected image, formedby the light reflected from the cornea of the eye 103, and images ofpupil etc. on an image sensor 9 such as a CCD, through the prism member3 and the dichroic mirror 7 of the optical member 10. The imaging lens 8is provided independently from the observation system for observing thefalse image of the image information of the display means 4. Theelements in the optical path from the light source means 102 to theimage sensor 9 by way of the eye 103 constitute a visual line detectingsystem for detecting the visual line of the eye 103 of the observer 101.In the present embodiment, the elements of the observation system andthe visual line detecting system are designed as explained in theforegoing, thereby facilitating the compactization of the entire systemincorporating these two systems.

In the following there will be explained, with reference to FIGS. 8A and8B, the observation system for observing the false image of the imageinformation displayed on the display means 4. In the present embodiment,a visible light beam based on the image information displayed on thedisplay means 4 is transmitted by the dichroic mirror face 7 of theoptical member 10 and is introduced into the prism member 3 through theentrance face 5 thereof. It is then totally reflected by the front face1 of the prism member 3, then reflected and condensed by the concaveface 2, further transmitted by the front face 1 and guided to the eye103 of the observer 101. In such configuration, the curvatures of thefront face 1 and the concave face 2 are so suitably selected that afalse image of the image information displayed on the display means 4 isformed in front of the observer 101, without a primary image plane forintermediate image formation.

As explained above, in the present embodiment, the observation system isconstructed as false image type, whereby the observer 101 observes thefalse image of the image information. It is also possible, in thepresent embodiment, to constitute the concave face 2 with asemi-transmitting surface and the rear face 6 with a transmittingsurface, and suitably selecting the curvature of the rear face 6,thereby spatially superimposing the external image information and thefalse image of the image information of the display means 4 forobservation in a same viewing field with same visibility.

In the observation system of the present embodiment, in displaying theimage information on the display means from the image information supplymeans such as a CD-ROM 105 or a video camera 106 held by the observer101 as shown in FIGS. 10 and 11, the visual line information of the eyeof the observer, obtained by the visual line detecting system, isutilized for various controls, such as auto focusing (focusing of thevideo camera), electronic zooming (electrical enlargement of theinformation in the direction of the visual line), zooming (calculationof the focal length f of the video camera for obtaining an image framesize extracted by the visual line and matching to said focal length),and menu selection (light metering, flash panorama size etc.) selectedby the visual line.

In the following there will be explained, with reference to FIG. 9, thevisual line detecting system for detecting the visual line of the eye103 of the observer 101. The eye 103 of the observer 101 is illuminatedwith the infrared light from the light source means 102, and theinfrared light reflected by the cornea of the eye 103 is transmitted bythe front face 1 of the prism member 3, then reflected by the concaveface 2, further totally reflected by the front face 1, transmitted bythe entrance face 5 and guided into the optical member 10. It is thenreflected by the dichroic mirror face 7 thereof, totally reflected by aface 10 a thereof and is guided to the image sensor 9 through theimaging lens 8.

The imaging lens 8 forms the corneal reflected image and the images ofthe pupil etc. of the eye 103 on the image sensor 9, and the visual lineof the eye 103 is detected from the signal of said image sensor 9.

In the present embodiment, the visual line of the eye is detected by amethod disclosed for example in the Japanese Patent laid-OpenApplication No. 1-274736 and Japanese Patent Application No. 3-11492 ofthe present applicant.

FIGS. 12A and 12B are schematic cross-sectional views of the prismmember 3 employed in the present embodiment. It is employed in this caseas an observation system, but, in case it is employed as the visual linedetecting system, the optical functions remain the same except that theoptical path is reversed. A light beam 4 a, perpendicularly emitted fromthe display face of the display means 4 is transmitted by the entranceface 5 of the prism member 3 and enters the toric aspherical front face1 with an incident angle at least equal to 43°, thereby being totallyreflected by said front 1. The light beam 4 a is then introduced intothe toric aspherical concave face 2 with an incident angle not exceeding43°, thereby being reflected by the concave face and is emitted from thefront face 1.

The front face 1 is curved, and effects total reflection in a part andtransmission in another part. It is therefore equivalent to two curvedsurfaces, and, in combination with the concave face 2, there isconstituted a reflective optical system having three curved surfaces. Inthis manner the focal length of the entire optical system is shortened(20 to 25 mm in the following numerical examples), whereby the entireoptical system can be compactized.

In the present embodiment, a toric surface, a toric aspherical surfaceor an anamorphic aspherical surface with variable refractive power, i.e.variable curvature, depending on the azimuthal angle is employed in thefront face 1, the concave face 2 and the entrance face 5 in theobservation system and the visual line detecting system 5, wherebysatisfactory correction is attained for the eccentric aberrationgenerated when the angle between the incident light and the emerginglight of the concave mirror 2 is made large in order to reduce the sizeof the entire optical system.

The curvatures of the front face 1 and the rear face 6 are so selectedas to constitute a meniscus lens having a small refractive power for thelight passing through these faces, whereby the external imageinformation such as the external scenery can be satisfactorily observedthrough the rear face 6.

Also in the cross section in the meridian direction, the front face 1 isgiven a negative refractive power, in order to correct the aberrationsgenerated by the positive refractive power of the concave face 2. Themeridian direction means a plane perpendicular to the plane containingthe optical path from the center of the image on the display means tothe designed center of the eye (i.e. direction perpendicular to theplane of FIGS. 12A and 12B).

Also in the present embodiment, the front face 1 may be given a negativerefractive power in the cross section in the generatrix direction, forattaining an effect similar to that of the negative refractive power inthe cross section in the meridian direction. The cross section in thegeneratrix direction means a plane containing the optical path from thecenter of the image of the display means to the designed center of theeye (i.e. plane of FIGS. 12A and 12B).

There is satisfied a condition:|α|≦20°  (1)wherein α is the tilt angle, as shown in FIG. 12B, between a tangentialline L at the vertex of the front face 1 in the cross section in thegeneratrix direction and a line m perpendicular to the optical axis 104of the eye and passing the vertex of the front face 1. As indicated bythe condition (1), the angle α is selected smaller than 20°, therebyreducing the distortion in observation of the false image of the imageinformation of the display means 4 and the external image informationsuch as external scenery in spatially superimposed state, and reducingthe thickness of the prism in the axial direction.

In the following there will be explained other features of theobservation system and the visual line detecting system including theelements (entrance face 5, front face 1 and concave face 2) provided inthe optical path from the display means 4 to the eye 103.

(2-1) In the present embodiment, the imaging magnification β of theimaging lens 8 from the eye 103 to the image sensor 9 is defined by:0.02<|β|<0.18  (2)Above the upper limit of the condition (2), the magnification of the eyeimage becomes too large, so that the effective diameter of the imagesensor becomes undesirably large. Also below the lower limit of thecondition (2), the focal length of the visual line detecting system hasto be made shorter, whereby various aberrations are generated and asatisfactory eye image cannot be obtained.

(2-2) Also there is satisfied a condition:0.9<|f _(y) /f _(x)|<1.1  (3)wherein f_(y), f_(x) are focal lengths of the entire system respectivelyin the generatrix cross section and the meridian cross section, therebymaintaining a substantially constant focal length for the entire systemin any azimuthal angle and dispensing with the correction for the aspectratio, in the generatrix direction and the meridian direction, of theimage information displayed on the display means.

(2-3) Also there is satisfied a condition:|R_(x)|<|R_(y)|  (4)wherein R_(y), R_(x) are radii of paraxial curvature of the concave face2 respectively in the generatrix cross section and the meridian crosssection. For compactizing the observation system, the optical axis ofthe concave face has to be significantly tilted clockwise, in thegeneratrix cross section, from the optical axis of the eye, but suchconfiguration generates a large eccentric aberration. On the other hand,in the meridian cross section, such eccentric aberration is notgenerated much because there is little room for such eccentricity. Inthe present embodiment, therefore, the radius R_(y) of curvature in thegeneratrix cross section is selected larger than that R_(x) in themeridian cross section as indicated by the condition (4), or therefractive power in the generatrix direction is selected weaker thanthat in the meridian direction, thereby suppressing the eccentricaberration in the generatrix cross section.

In the present embodiment, for the purpose of correction of theeccentric aberration, the condition (4) is preferably set as follows:|R _(x) /R _(y)|<0.85  (5)

(2-4) When the entrance face 5 of the prism member 3 is constituted by atoric surface or an anamorphic surface, there is selected a condition:|R_(y5)|<|R_(x5)|  (6)wherein R_(y5) and R_(x5) are radii of curvature respectively in thegeneratrix cross section and the meridian cross section. The entranceface 5 generates relatively little eccentric aberration in thegeneratrix cross section. Thus, though the concave face 2 and the frontface 1 cannot be given strong refractive forces in the generatrix crosssection, the entrance face 5 is given a strong refractive force in thegeneratrix cross section, thereby realizing a substantially constantfocal length in any azimuthal angle in the entire system.

(2-5) Satisfactory optical performance is realized in the meridian crosssection by giving a negative refractive power to the totally reflectingarea of the front face 1, a positive refractive power to the concaveface 2 and a negative refractive power to the transmitting area of thefront face 1. In case the entrance face 5 has a refractive power, it ispreferably selected as positive in the generatrix cross section, inorder to cover the deficiency in the positive refractive power in thegeneratrix cross section in the entire system.

(2-6) Satisfactory optical performance is realized in the generatrixcross section by giving a negative refractive power in the totallyreflecting area of the front face 1, and a positive refractive power tothe concave face 2. In case the entrance face 5 has a refractive power,it is selected as positive in the meridian cross section, therebyreducing the aberrations in the meridian cross section.

(2-7) In the meridian cross section, there are satisfied condition:0.1<|2f _(x) /R _(x1)|<2.0  (7)0.5<|2f _(x) /R _(x2)|<2.5  (8)wherein R_(x1), R_(x2) are radii of curvature respectively of thetotally reflecting area of the front face 1 and of the concave face 2,and f_(x) is the focal length of the entire system. The upper limits ofthe conditions (7), (8) correspond to stronger refractive forces of saidcurvatures, while the lower limits correspond to the weaker refractiveforces. Above the upper limit of the condition (7), the distortionaberration becomes difficult to correct, and, below the lower limit, thetotally reflecting condition becomes difficult to satisfy. Also abovethe upper limit of the condition (8), the astigmatism becomes difficultto correct, and, below the lower limit, the entire optical systembecomes larger, particularly with a larger thickness in the directionparallel to the optical axis.

(2-8) In the generatrix cross section, there are satisfied condition:0<|2f _(y) /R _(y2)|<1.0  (9)0.2<|2f _(y) /R _(y2)|<2.5  (10)wherein R_(y1), R_(y2) are radii curvature respectively of the totallyreflecting area of the front face 1 and the concave face 2, and f_(y) isthe focal length of the entire system. The upper limits of theconditions (9) and (10) correspond to stronger refractive powers of saidcurvatures, while the lower limits correspond to weaker refractivepowers. Above the upper limit of the condition (9), the eccentricdistortion aberration becomes difficult to correct, while, below thelower limit, it becomes difficult to satisfy the totally reflectingcondition. Also above the upper limit of the condition (10), eccentricastigmatism is generated significantly, and, below the lower limit, thelength of the entire lens increases and the entire optical systembecomes undesirably bulky.

(2-9) The concave face 2 is shifted in parallel manner, in thegeneratrix cross section (Y-direction), from the optical axis 104 of theeye toward the display means 4, thereby suppressing the eccentricdistortion aberration in the generatrix cross section. The amount E ofparallel shift (distance from the optical axis 104 to the vertex of theconcave face 2 as shown in FIG. 12B) is so selected as to satisfy:25≦E  (11)thereby satisfactorily correcting the eccentric distortion.

(2-10) The tilt angle α in the condition (1) is so maintained as tosatisfy:−15°≦α≦5°  (12)for effectively compactizing the entire optical system. Below the lowerlimit of the condition (12), the image information becomes distortedsignificantly, while, above the upper limit, the prism member 3 becomesthicker in the direction of the optical axis 104.

FIGS. 13 to 16 are schematic views showing modifications in a part ofthe visual line detecting system in the vicinity of the prism member 3.

An embodiment shown in FIG. 13 is different from the foregoingembodiments in that the optical member 10 is provided between the eye103 of the observer and the prism member 3, with correspondingpositioning of the imaging lens 8 and the image sensor 9. Thisembodiment provides an advantage of exact detection of the visual line,since no eccentric face is involved in the visual line detecting system.

In an embodiment shown in FIG. 14, the dichroic face 7 is provided ininclined manner inside the prism member 3, with correspondingpositioning of the imaging lens 8 and the image sensor 9. Thisembodiment is featured by a reduced number of components, leading tofurther compactization of the entire optical system.

In an embodiment shown in FIG. 15, the optical member 10 is positionedfarther than the prism member 3 from the eye 103. Also the concave face2 is provided with a dichroic film reflecting the visible light andtransmitting the infrared light. The optical member 10 is provided withan inclined reflecting face 11, having a semi-transmitting, totallyreflecting or dichroic film, and the imaging lens 8 and the image sensor9 are positioned accordingly. The state of mounting of the device of thepresent embodiment, on the head of the observer, is schematicallyillustrated in FIGS. 17A and 17B.

In an embodiment shown in FIG. 16, the optical member 10 consisting of aparallel-faced flat plate is replaced by a dichroic mirror 7,transmitting the visible light and reflecting the infrared light,provided on the entrance face 5 of the prism member 3, and the imaginglens 8 and the image sensor 9 are positioned accordingly. The state ofmounting of the device of the present embodiment, on the head of theobserver, is schematically illustrated in FIGS. 18A and 18B.

Display devices utilizing the visual line detecting systems of theabove-explained embodiments can be directly applied to so-called head-updisplay device.

In the following there are shown numerical examples of the presentembodiment, wherein elements of the system are represented as follows,with reference to FIGS. 8A, 8B and 9:

(1) eye 103 being selected as the original point (0,0) of the coordinatesystem;

(2) in the visual line detecting system, in tracing the light from theeye 103;

-   -   i==1 eye    -   i=2 front face 1 (transmitting face)    -   i=3 concave face 2    -   i=4 front face (totally reflecting face)    -   i=5 entrance face 5    -   i=6 entrance face of optical member 10    -   i=7 dichroic face    -   i=8    -   i=9 exit face of optical member 10    -   i=10 entrance face of imaging lens    -   i=11 exit face of imaging lens    -   i=12 image sensor    -   in the observation system;    -   i=8 entrance face of image information    -   i=9 display face of image information

(3) TAL indicates a toric aspherical surface; and AAL indicates ananamorphic aspherical surface.

The TAL is defined, in the generatrix (Y-Z) cross section, by thefollowing aspherical equation:

$Z = {\frac{y^{2}/{ryi}}{1 + \sqrt{1 - {\left( {1 + {ki}} \right)\left( {y/{ryi}} \right)^{2}}}} + {Aiy}^{4} + {Biy}^{6} + {Ciy}^{8} + {Diy}^{10}}$wherein i indicates the face number, and is spherical in the meridian(X-Z) cross section.

Also the AAL is defined by:

$Z = \frac{\left( {{y^{2}/{ryi}} + {x^{2}/{ryi}}} \right)}{1 + \sqrt{\begin{matrix}{1 - \left\{ {{\left( {1 + {kyi}} \right)\left( {y/{ryi}} \right)^{2}} + {\left( {1 + {kxi}} \right)\left( {x/{rxi}} \right)^{2}}} \right\} + {{ARi}\left\{ {{\left( {1 + {APi}} \right)y^{2}} +} \right.}} \\{\left. {\left( {1 - {APi}} \right)x^{2}} \right\}^{2} + {{BRi}\left\{ {{\left( {1 + {BPi}} \right)y^{2}} +} \right.}} \\{\left. {\left( {1 - {BPi}} \right)x^{2}} \right\}^{3} + {{CRi}\left\{ {{\left( {1 + {CPi}} \right)y^{2}} + {\left( {1 - {CPi}} \right)x^{2}}} \right\}^{4}} +} \\\left. {{{DRi}\left\{ {1 + {DPi}} \right)y^{2}} + {\left( {1 - {DPi}} \right)x^{2}}} \right\}^{5}\end{matrix}}}$wherein i indicates the face number.

Also in the present invention, AL indicates a rotationally symmetricalaspherical surface, which is defined by:

$Z = {\frac{y^{2}/{ryi}}{1 + \sqrt{1 - {\left( {1 + {ki}} \right)\left( {y/{ryi}} \right)^{2}}}} + {Aiy}^{4} + {Biy}^{6} + {Ciy}^{8} + {Diy}^{10}}$wherein i indicates the face number. The surface vertex coordinate (Y,Z) is an absolute coordinate when the vertex of the eye surface is takenas (0,0). The tilt angle in the generatrix cross section indicates thetilt angle of the optical axis of each face, with respect to the opticalaxis of the eye, said angle being taken positive anticlockwise. Areflecting face (including totally reflecting face) is indicated by asuffix M. nd and vd respectively indicate the refractive index and theAbbe's number for d-line.

NUMERICAL EXAMPLE 5

(Visual line detecting system) r_(yi) r_(xi) Radius of Radius ofcurvature curvature Tilt angle in in generatrix in meridian Vertexgeneratrix cross section cross section coordinate Y, Z cross section i =1 ∞ (0, 0) 0° eye i = 2 −514.575 −52.805 (0, 21.15) 0 TAL i = 3 −63.546−42.575 (26.30, 35.96) −3.33 TAL-M nd = 1.49171 i = 4 −514.575 −52.805(0, 21.15) 0 TAL-M {close oversize bracket} νd = 57.4 i = 5 ∞ (20.72,28.06) 65.37 i = 6 ∞ (21.18, 28.27) 65.37 i = 7 ∞ (23.41, 28.20) 30.37 Mnd = 1.51633 i = 8 ∞ (21.18, 28.27) 65.37 M {close oversize bracket} νd= 64.1 i = 9 ∞ (24.93, 20.09) −54.64 i = 10 −1.889 (26.90, 21.14) −54.64AL nd = 1.49171 {close oversize bracket} i = 11 1.426 (29.35, 19.41)−54.64 AL 84 d = 57.4. i = 12 ∞ (30.51, 18.95) −51.60 image sensor(Observation system) nd = 1.51633 i = 8 ∞ (23.91, 29.52) 65.37 {closeoversize bracket} νd = 64.1 i = 9 ∞ (24.98, 30.01) 59.37 image infor-mation (TAL, AL data) TAL2,4: K = 460.670, A = −0.227E−5, B = 0.179E−7,C = −0.453E−10, D = 0.429E−13 TAL3 K = 1.105, A = −0.709E−6, B =−0.273E−8, C = −0.191E−11, D = 0.631E−15 AL10: K = −3.858, A = 0.851E−2,B = −0.101, C = 0.149, D = −0.755E−1 AL11: K = −0.113, A = 0.195, B =−0.590, C = 0.471, D = −0.138 (1) α = 0 (5) |Rx1/Ry1| = 0.10 (8) 2fx/Rx2= −1.09 (11) E = 26.3 (2) | β | = 0.10 |Rx2/Ry2| = 0.67 (9) 2fy/Ry1 =−0.04 (3) | fy/fx | = 1.00 (7) 2fx/Rx1 = −0.88 (10) 2fy/Ry2 = −0.36

NUMERICAL EXAMPLE 6

(Visual line detecting system) r_(yi) r_(xi) Radius of Radius ofcurvature curvature Tilt angle in in generatrix in meridian Vertexgeneratrix cross section cross section coordinate Y, Z cross section i =1 ∞ (0, 0) 0° eye i = 2 −514.575 −52.805 (0, 21.15) 0 TAL i = 3 −63.546−42.575 (26.30, 35.96) −3.33 TAL nd = 1.49171 i = 4 −514.575 −52.805 (0,34.15) 0 TAL {close oversize bracket} νd = 57.4 i = 5 ∞ (0, 37.15) 45 Mi = 6 −1.889 −(13.0, 37.15) 90 AL nd = 1.49171 {close oversize bracket}i = 7 1.426 (−16.0, 37.15) 90 AL νd = 57.4 i = 8 ∞ (−17.27, 37.15) 90image sensor (Observation system) i = 3 −63.546 −42.575 (26.30, 35.96)−3.33 TAL-M nd = 1.51633 i = 4 −514.575 −52.805 (0, 21.15) 0 TAL-M{close oversize bracket} i = 5 ∞ (20.72, 28.06) 65.37 νd = 64.1 i = 6 ∞(24.05, 29.59) 54.25 image infor- mation (TAL, AL data) TAL2,4: K =460.670, A = −0.227E−5, B = 0.179E−7, C = −0.453E−10, D = 0.429E−13 TAL3K = 1.105, A = −0.709E−6, B = 0.273E−8, C = −0.191E−11, D = 0.631E−15AL6: K = −3.858, A = 0.851E−2, B = −0.101, C = 0.149, D = −0.755E−1 AL7:K = −0.113, A = 0.195, B = −0.590, C = 0.471, D = −0.138 (1) α = 0 (5)|Rx1/Ry1| = 0.10 (8) 2fx/Rx2 = −1.09 (11) E = 26.3 (2) | β | = 0.05|Rx2/Ry2| = 0.67 (9) 2fy/Ry1 = −0.04 (3) | fy/fx | = 1.00 (7) 2fx/Rx1 =−0.88 (10) 2fy/Ry2 = −0.36

NUMERICAL EXAMPLE 7

(Visual line detecting system) r_(yi) r_(xi) Radius of Radius ofcurvature curvature Tilt angle in in generatrix in meridian Vertexgeneratrix cross section cross section coordinate Y, Z cross section i =1 ∞ (0, 0) 0° eye i = 2 −2158.074 −32.224 (0.60, 19.85) −10.55 AAL i = 3−63.157 −32.870 (34.76, 30.92) 15.81 AAL-M nd = 1.49171 i = 4 −2158.074−32.224 (0.60, 19.83) −10.55 AAL-M {close oversize bracket} νd = 57.4 i= 5 72.108 1049.744 (14.82, 29.02) 53.74 AAL i = 6 ∞ (14.98, 29.14)53.74 i = 7 ∞ (17.19, 29.51) 18.74 M nd = 1.51633 i = 8 ∞ (14.98, 29.14)53.74 M {close oversize bracket} νd = 64.1 i = 9 ∞ (20.31, 21.88) −66.27i = 10 −1.889 (22.03, 23.31) −66.27 AL nd = 1.49171 {close oversizebracket} i = 11 1.426 (24.77, 22.10) −66.27 AL νd = 57.4. i = 12 ∞(25.96, 21.91) −63.23 image sensor (Observation system) nd = 1.51633 i =8 ∞ (17.40, 30.91) 53.74 {close oversize bracket} νd = 64.1 i = 9 ∞(18.21, 31.50) 44.74 image infor- mation (AAL, AL data) AAL2,4: Ky =−13763.5, AR = −0.170E−4, BR = 0.401E−7, CR = −0.154E−9, DR = 0.223E−12Kx = −3.896, AP = −0.245, BP = 0.416E−1, CP = 0.870E−1, DP = −0.203E−1AAL3: Ky = 1.238, AR = −0.317E−5, BR = 0.248E−8, CR = −0.179E−11, DR =0.608E−15 Kx = 0.279, AP = +0.249, BP = 0.327E−2, CP = −0.192E−1, DP =0.181E−1 AAL5: Ky = 6.285, AR = −0.114E−4, BR = −0.402E−6, CR =0.113E−8, DR = −0.411E−10 Kx = −1.33E−6, AP = 0.273E+1, BP = 0.155E+1,CP = 0.160E+1, DP = −0.644 AL10: K = −3.858, A = 0.851E−2, B = −0.101, C= 0.149, D = −0.755E−1 AL11: K = −0.113, A = 0.195, B = −0.590, C =0.471, D = −0.138 (1) α = −10.5 (5) |Rx1/Ry1| = 0.01 (8) 2fx/Rx2 = −1.47(11) E = 34.8 (2) | β | = 0.12 |Rx2/Ry2| = 0.52 (9) 2fy/Ry1 = −0.02 (3)| fy/fx | = 0.96 (7) 2fx/Rx1 = −1.5 (10) 2fy/Ry2 = −0.73

NUMERICAL EXAMPLE 8

(Visual line detecting system) r_(yi) r_(xi) Radius of Radius ofcurvature curvature Tilt angle in in generatrix in meridian Vertexgeneratrix cross section cross section coordinate Y, Z cross section i =1 ∞ (0, 0) 0° eye i = 2 −9423.260 −47.769 (0, 20.38) 1.50 AAL i = 3−65.701 −36.469 (33.13, 29.99) 14.29 AAL-M nd = 1.49171 i = 4 −9433.260−47.769 (0, 20.38) 1.50 AAL-M {close oversize bracket} νd = 57.4 i = 57188.930 −49.971 (16.33, 26.54) 62.55 AAL i = 6 ∞ (19.89, 27.27) 21.55 Mi = 7 −1.889 (21.28, 20.34) −11.45 AL nd = 1.49171 {close oversizebracket} i = 8 1.426 (21.88, 17.39) −11.45 AL νd = 57.4 i = 9 ∞ −8.45image sensor (Observation system) i = 7 ∞ (21.11, 29.03) 55.43 imageinfor- mation (AAL, AL data) AAL2,4: Ky = −361850, AR = −0.183E−4, BR =0.381E−7, CR = −0.114E−9, DR = 0.153E−12 Kx = −13.802, AP = −0.317, BP =−0.602E−1, CP = 0.272E−1, DP = −0.211E−1 AAL3: Ky = 1.227, AR =−0.209E−5, BR = 0.308E−8, CR = −0.190E−11, DR = 0.505E−15 Kx = 0.172, AP= 0.472, BP = 0.553E−1, CP = −0.265E−1, DP = 0.751E−2 AAL5: Ky = 987000,AR = −0.871E−5, BR = −0.264E−6, CR = 0.469E−13, DR = 0.137E−11 Kx =−70.169, AP = 41.763, BP = −0.395, CP = 0.183E+2, DP = −0.988 AL7: K =−3.858, A = 0.851E−2, B = −0.101, C = 0.149, D = −0.755E−1 AL8: K =−0.113, A = 0.195, B = −0.590, C = 0.471, D = −0.138 (1) α = 1.5 (5)|Rx1/Ry1| = 0.005 (8) 2fx/Rx2 = −1.22 (11) E = 33.1 (2) | β | = 0.10|Rx2/Ry2| = 0.56 (9) 2fy/Ry1 = −0.46 (3) | fy/fx | = 1.00 (7) 2fx/Rx1 =−0.93 (10) 2fy/Ry2 = −0.61

NUMERICAL EXAMPLE 9

(Visual line detecting system) r_(yi) r_(xi) Radius of Radius ofcurvature curvature Tilt angle in in generatrix in meridian Vertexgeneratrix cross section cross section coordinate Y, Z cross section i =1 ∞ (0, 0) 0° eye i = 2 −9538.246 −47.590 (0, 21.30) 7.28 AAL i = 3−65.6 −36.035 (32.96, 31.40) 14.67 AAL-M {close oversize bracket} nd =1.49171 i = 4 −9538.246 −47.590 (0, 21.30) 0.28 AAL-M νd = 57.4 i = 5225.188 727.642 (16.47, 28.45) 65.28 AAL i = 6 ∞ (16.92, 28.60) 67.28 i= 7 ∞ (19.15, 28.51) 35.28 M nd = 1.51633 i = 8 ∞ (16.92, 28.66) 67.28 M{close oversize bracket} νd = 64.1 i = 9 ∞ (19.69, 29.82) 67.28 M i = 10∞ (23.55, 20.60) −167.72 i = 11 1.889 (21.38, 20.05) −167.72 AL nd =1.49171 {close oversize bracket} i = 12 −1.426 (20.74, 17.12) −167.72 ALνd = 57.4 i = 13 ∞ (20.19, 16.01) −164.69 image sensor (Observationsystem) nd = 1.51633 i = 8 ∞ (19.69, 29.82) 67.28 {close oversizebracket} νd = 64.1 i = 9 ∞ (22.02, 29.17) 54.10 image infor- mation(AAL, AL data) AAL2,4: Ky = −387540, AR = −0.183E−4, BR = 0.378E−7, CR =−0.117E−9, DR = 0.158E−12 Kx = −20.897, AP = −0.300, BP = −0.548E−1, CP= 0.326E−1, DP = −0.228E−1 AAL3: Ky = 1.213, AR = −0.224E−5, BR =0.305E−8, CR = −0.190E−11, DR = 0.500E−15 Kx = 0.165, AP = −0.464, BP =0.630E−1, CP = −0.251E−1, DP = 0.380E−2 AAL5: Ky = 559.028, AR =−0.675E−5, BR = 0.182E−6, CR = 0.212E−12, DR = −0.189E−10 Kx = −99429.4,AP = 0.486E+1, BP = −0.125E+1, CP = 0.111E+2, DP = −0.789 AL11: K =−3.858, A = 0.851E−2, B = −0.101, C = 0.149, D = −0.755E−1 AL12: K =−0.113, A = 0.195, B = −0.590, C = 0.471, D = −0.138 (1) α = 0.28 (5)|Rx1/Ry1| = 0.005 (8) 2fx/Rx2 = −1.26 (11) E = 33.0 (2) | β | = 0.11|Rx2/Ry2| = 0.55 (9) 2fy/Ry1 = −0.005 (3) | fy/fx | = 1.00 (7) 2fx/Rx1 =−0.95 (10) 2fy/Ry2 = −0.69

According to the present invention, as explained in the foregoing, thereis provided a display device, such as a head-mount display, enablingcompactization and provided with a visual line detecting system capableof controlling, based on the visual line information, the observationstate of the image information displayed by the display means in theobservation system, by suitably designing said observation system forobserving the image information displayed by the display means and thevisual line detecting system provided, in a part of the observationsystem, for detecting the visual line of the observer.

In the following there will be explained the control of the displaydevice utilizing the above-explained visual line detecting function.

FIGS. 19A and 19B show the optical paths respectively of the observationsystem and the visual line detecting system in the optical system of thepresent invention.

Display means 4 displays, on a display face thereof, an image such as acharacter or a pattern, with visible light. A flat prism 10 is composedof two adhered prisms, of which junction plane is provided with adichroic mirror transmitting the visible light and reflecting theinfrared light for visual line detection. The prism 10 has a lateralwall 13.

A first optical member 3A is provided with a flat face 5, a curved oraspherical face 1, and a half-transmitting or totally reflecting,spherical or aspherical face 2 a of a positive refractive power. In thepresent embodiment, the face 2 a is composed of a half mirror. A secondoptical member 3B is provided with a transparent or opaque, flat orcurved face 6, and a concave face 2 b, consisting of a half-transmittingor totally reflecting, spherical or aspherical surface same in shape asthe face 2 a. The face 2 a of the first optical member 3A and the face 2b of the second optical member 3B are adhered to constitute a singleprism block 3. The adhered face 2 constitutes a half mirror.

There are also provided an imaging lens 8 for visual line detection, animage sensor 9 consisting of a CCD, and a light source 12 for detectingthe visual line of the eye E of the observer, by illuminating thefrontal part of said eye E with invisible (infrared) light.

A visual line detecting circuit 14 detects the visual line informationof the eye E. Discrimination means 15 discriminates whether the visualline of the observer is fixed for a predetermined time in asubstantially same direction. Control means 16 receives image signalsfrom an image information source S and displays an image on the displayface of the display means 4 under controlled display state based on thevisual line information from the discrimination means 15.

The prism 10 and the first optical member 3A constitute a part of theimage observation optical system, and the image observation opticalsystem and the second optical member 3B constitute a part of theobservation optical system.

In the following there will be explained, with reference to FIG. 19A,the function of the observation optical system of the presentembodiment. The control means 16 displays the image on the display faceof the display means 4, based on the signals from the image informationsource S. The light beam (visible light beam) from the image displayedon the display means 4 is transmitted by the dichroic mirror 7 of theprism 10, then introduced into the prism block 3 through the face 5,totally reflected by the face 1, then reflected and condensed by thehalf mirror surface 2, and emerges from the face 1 to enter the pupil 0of the observer. Thus a false image Y of the image displayed on thedisplay means 4 is formed in front of the observer, and can be observedby the observer.

On the other hand, the light beam from the external scenery G isintroduced into the face 6 of the prism block 3, then transmitted by thehalf mirror 2 and emerges from the face 1 to reach the pupil of theobserver, who can thus observe the external scenery. Thus the observerobserves, within a same viewing field, the false image Y of the imagedisplayed on the display means 4 and the external scenery insuperposition.

In the following there will be explained the function of the visual linedetecting optical system of the present embodiment. Referring to FIG.17B, the light reflected and scattered by the frontal part of the eye Eof the observer, illuminated by the infrared light from the light source12, is introduced into the face 1 of the prism block 3, then reflectedby the half mirror 2 toward the face 1, then totally reflected by theface 1 and emerges from the face 5 to enter the prism 10. It is thenreflected by the dichroic mirror 7, totally reflected by the lower faceof the prism 10 and emerges from the face 13. It is then transmitted bythe imaging lens 8 for visual line detection, thereby forming an imageof the frontal part of the eye on the image sensor 9. The lightreflected by the cornea of the eye E forms Purkinje's images, while thelight scattered by the pupil forms an image of the pupil. The visualline detecting circuit 14 calculates the direction of the visual line ofthe observer, based on the Purkinje's images and the pupil imageobtained from the image sensor 9. This detection can be achieved forexample by a method disclosed in the Japanese Patent Laid-OpenApplication No. 3-109029 of the present applicant.

The light source 12, the first optical member 3A, the prism 10, theimaging lens 8, the image sensor 9 and the visual line detecting circuit13 constitute a part of the visual line detecting means.

FIG. 20 is a flow chart showing the control sequence of the presentinvention, for arbitrarily and selectively varying the size and positionof the false image of the displayed image, to be superimposed with theexternal image, by the control means 16 of the present inventionaccording to the visual line information of the eye E of the observer.

FIG. 21 is a schematic view of display areas, i.e. size and position ofthe display, selectable in the image display on the display means 4. Inthis embodiment there are selectable five display areas 1 to 5, in which1 to 4 respectively correspond to rectangular areas, each equal to ¼ ofthe display face, while 5 corresponds to the full display face.

In the following there will be explained the steps of the flow chart.The drawings at the right indicate the images provided to the observerat the respective steps.

In the present embodiment, the direction of the visual line of theobserver is constantly detected.

Step 21: Turns on a switch for activating the function of the presentinvention. For this purpose, a switch mark is displayed, at apredetermined position within the display face, during the ordinaryimage observation, and, if the observer watches the false image of theswitch mark for a predetermined time, the visual line detecting meansand the discrimination means 15 detect such watching state and initiatea switching operation of the displayed image in the following sequence:

(1) The visual line detecting means detects the direction watched by theobserver.

If the position of the visual line coincides with the switch mark or thevicinity thereof, the discrimination means 15 stores the direction ofthe visual line, as first visual line information, in a memory, and thesequence proceeds to (2).

If the detected direction does not coincide with the switch mark, thediscrimination means identifies that the observer does not wish toswitch the displayed image, so that the sequence does not proceed to(2).

(2) After the lapse of a predetermined time, the discrimination means 15detects, by the visual line detecting means, the direction watched bythe observer.

If the detected direction coincides with the switch mark, thediscrimination means 15 judges that the observer has watched the switchmark for the predetermined time, and sends a signal to the control means16 to turn on the switch. Then the sequence proceeds to a step 22.

On the other hand, if the detected direction does not coincide with theswitch mark, the sequence returns to (1).

By repeating the above-explained steps, the switching operation for thedisplayed image is securely started when the observer watches the switchmark for the predetermined time.

Step 22: When the switch is turned on, the control means 16 displays,for example, five points shown in FIG. 22, on the display face of thedisplay means 4. Thus the observer sees an image 22 a in FIG. 20.

Step 23: Determines the display area. The observer watches a point,representing the desired display area, for a predetermined time, and thevisual line detecting means and the discrimination means 15 identifiesthe point watched by the observer for the predetermined time, within theimage 22 a, in the following sequence:

(1) The visual line detecting means detects the direction watched by theobserver, and the discrimination means 15 identifies whether thedetected direction coincides with any of the five points. If thedetected direction coincides with any of the points, the detecteddirection or position is stored, as first visual line information, in amemory.

If the detected direction does not coincide with any of the points, thedetection of the visual line is continued until the visual line isdetected to any of the points.

(2) After the lapse of a predetermined time, the discrimination means 15detects, by the visual line detecting means, the direction watched bythe observer, and obtains second visual line information.

(3) The discrimination means 15 compares the detected direction ofvisual line with that corresponding to the point stored in the memory.

If two directions mutually coincide, the discrimination means judgesthat the point corresponding to the detected direction is the pointdesired by the observer for image display and sends the correspondinginformation to the control means 16, and the sequence proceeds to a step24.

If the two directions do not mutually coincide, the sequence returns to(1).

The point watched by the observer is determined by repeating theabove-explained steps.

In this manner, when the observer watches a point for a predeterminedtime, a display area is uniquely determined corresponding to said point.

Step 24: The control means 16 displays an image in the display areadetermined in the step 23, by varying the size and position of thedisplay of the image, by applying suitable image processing to the imageinformation. For example, if the point 5 shown in FIG. 21 is selected,the image is displayed in full size of the display face. If the point 4is selected, the image size is changed to ¼ of the display face and isdisplayed at the lower right part thereof, as shown in 24 a. However theswitch mark is separately displayed anew.

The switching of the displayed image is thus completed.

In the present embodiment, as explained in the foregoing, the size andposition of the false image of the displayed image to be superimposedcan be varied, in the course of image observation and according to thesituation of the external image, by merely directing the visual line ofthe observer to a specified position within the viewing field, withoutany manual operation, so that there is attained extremely satisfactoryoperability. Besides, in the present embodiment, the entire device canbe compactized by partial common use of the image observation opticalsystem for observing the displayed image and the visual line detectingoptical system for visual line detection.

In the foregoing embodiment the display area can be selected in fivemanners, but it is also possible to further increase the freedom ofselection available to the observer.

Also the switch turn-on operation may be conducted manually.

FIGS. 23A and 23B are respectively schematic views showing optical pathsin an observation optical system and a visual line detecting opticalsystem in another optical system of the present invention, whereincomponents same as those in FIGS. 19A and 19B are represented by samenumbers.

The present embodiment is different from that shown in FIGS. 19A and 19Bin that a transmissive liquid crystal device (shield member) 11 isprovided outside the face 6 of the second optical member in order tointercept the light beam, or a part thereof, entering the prism block 3from the outside. Such interception of the incoming light eliminates theoverlapping of the external image with the false image Y of thedisplayed image, thereby enabling clear observation of the latter.

The prism 10, the first optical member 3A etc. constitute a part of theimage observation optical system, while the image observation opticalsystem, the second optical member 3B and the liquid crystal device 11constitute a part of the observation optical system. Also the lightsource 12, the first optical member 3A, the prism 10, the imaging lens8, the image sensor 9 and the visual line detecting circuit 14constitute a part of the visual line detecting means.

The function of displayed image observation by the image observationoptical system and that of the visual line detecting optical system inthe present embodiment are same as that in the foregoing embodimentshown in FIGS. 19A and 19B.

In the following there will be explained the control sequence of thepresent embodiment, with reference to a flow chart shown in FIG. 24. Thedrawings at the right-hand side of the flow chart schematicallyillustrate the images provided to the observer in the respective steps.

In the present embodiment, the direction of visual line of the observeris constantly detected.

Step 61: Turns on a switch for activating the function of the presentinvention. As in the foregoing embodiment, when the observer watches,for a predetermined time, a false image of a switch mark displayed as aspot in a part of the displayed image, superimposed with the externalimage, the visual line detecting means and the discrimination means 15detect such watching state and initiate a switching operation of thedisplayed image.

Step 62: Enters the display size information of the displayed image. Thecontrol means 16 displays, for example, a false image of a displayedimage 62 a, for observation by the observer. Said image includes, forexample, a full-sized rectangular display frame S1, a rectangular frameS2 which is ½ in size in the vertical and horizontal directions, and arectangular frame S3 which is ¼ in size.

Each display frame has a watching mark at a corner (upper right cornerin the illustrated example). When the observer watches, for apredetermined time, the watching mark belonging to a desired frame, thevisual line detecting means and the discrimination means 15 detect suchwatching state and judge that the observer has selected thecorresponding display size, whereupon the display size is determined andthe corresponding information is supplied to the control means 16. (Thesequence for this operation is similar to that already explained in thestep 23 of the foregoing embodiment.) Such selecting procedure from alimited number of display frames enables rapid setting of the displaysize, though fine adjustment of the display size is not possible. As anexample, let us consider a case of selecting the frame S2.

Step 63: Enters the display position information of the displayed image.The control means 16 displays, for example, a false image of a displayedimage 63 a, in which the full-sized display face is divided intograting-patterned areas of a suitable number, in superposition with theexternal image. Then the observer watches, for a predetermined time, adesired image display position (for example marked with “x”) in theseareas. In response, the visual line detecting means and thediscrimination means 15 determine the display position in the followingsequence:

(1) The visual line detecting means detects the position watched by theobserver in the grating pattern, and the discrimination means 15 storesthe detected area number, as first visual line information, in a memory.

(2) After the lapse of a predetermined time, the discrimination means 15detects, by the visual line detecting means, the position watched by theobserver in the grating pattern, and the detected area number is takenas second visual line information.

(3) The discrimination means 15 compares thus detected area number withthat stored in the memory.

If the two area numbers mutually coincide, the discrimination means 15judges this area as the image display area desired by the observer, andsends the corresponding information to the control means 16. Then thesequence proceeds to a step 64.

If the two area numbers do not coincide with each other, the memorizedarea number is replaced by the newly detected area number, and thesequence returns to (2).

The display position desired by the observer is determined by repeatingthe above-explained steps. This procedure enables secure entry of theposition information and avoids erroneous input, even if the visual lineof the observer is somewhat shifted, as long as the observer watches thevicinity of the desired area for a predetermined time during the inputstate of the position information.

Step 64: The control means 16 discriminates whether the image of thedesignated size can be displayed around the display position designatedby the observer.

If such display is possible, the display area is thus determined and thesequence proceeds to a step 65.

On the other hand, if the displayed image P1 a around the designatedposition overflows the display face as indicated in 64 a, the sequenceproceeds to a step 66.

Step 66: Effects calculation for shifting the display position of thedisplayed image P1, for determining a display area P2, allowing toretain the designated size of the image P1 with a minimum shift of thedisplay position.

Step 65: The control means 16 shifts the transmittance of the liquidcrystal device 11 to zero in the image overlapping portion as indicatedin 65 a, thereby shielding the external image in said portion andavoiding the interference of the external image with the false image ofthus determined display image.

Step 67: The control means 16 displays the image in the display areadetermined in the steps 64 and 66, by varying the size and position ofdisplay of the image by applying suitable image processing to the imageinformation. The switch mark is displayed separately from theoverlapping area.

The switching of the displayed image is thus completed.

In the present embodiment, as explained in the foregoing, the size andposition of the false image of the displayed image to be superimposedcan be varied, in the course of image observation and according to thesituation of the external image, by merely directing the visual line ofthe observer to a specified position within the viewing field, and theexternal image in the superimposed portion is suitably shielded by ashield member. Thus there is attained an observation optical device,featured by extremely satisfactory operability, not requiring any manualoperation for varying the displayed image, and allowing clearobservation of the false image Y of the displayed image.

The display size may also be entered for example by displaying a linearpattern, of which an end corresponds to the full-sized image frame whilethe other end corresponds to the ¼-sized image frame, and judging thedisplay size desired by the observer in analog manner, based on theposition watched by the observer on the linear pattern. In this mannerthe observer can enter, in considerably precise manner, the proportionof display size with respect to the maximum display size.

In the present embodiment, a grating pattern is displayed at the entryof the display position, but such grating pattern display may bedispensed with.

Based on the above-explained configuration, the present inventionprovides an observation optical device of excellent operability capableof arbitrarily varying the size and position of display of the falseimage for observation of the image displayed on the display face, in thecourse of observation of such false image or of observation of suchfalse image spatially overlapped with the external image, to specifiedpositions within the viewing field, according to the wish of theobserver or to the external situation, utilizing the visual line of theobserver.

Furthermore there is provided an observation optical device capable ofshielding a part of the external image where the false image of thedisplayed image is overlapped, thereby enabling extremely clearobservation of such false image.

1. An optical apparatus comprising: means for forming an image to beobserved; and an ocular optical system for leading said image to anobserver's eyeball, said ocular optical system including, in order fromsaid image side, a third surface which forms an entrance surface, afirst surface which forms both a reflecting surface and an exit surface,and a second surface which forms a reflecting surface, said first tothird surfaces being integrally formed with a medium disposedtherebetween, wherein said means for forming an image is an imagedisplay device for forming an image for observation, said device beingdisposed at a position facing said third surface, said optical apparatusfurther comprising means for fitting both said device and said ocularoptical system to an observer's head, wherein at least said firstsurface in said ocular optical system is formed from a rotationallyasymmetric curved surface so as to correct aberrations produced by adecentered surface having an optical action.
 2. An optical apparatusaccording to claim 1, a combination of said device and said ocularoptical system being provided for each of observer's left and righteyeballs so as to lead an image to each of the observer's left and righteyeballs.
 3. An optical apparatus according to claim 2, furthercomprising: a see-through optical system disposed in the vicinity of thesecond surface of said ocular optical system to transmit a bundle oflight rays from an outside world and lead it to the second surface ofsaid ocular optical system; and a shutter provided at a side of saidsee-through optical system which is closer to the outside world, saidshutter allowing light to be selectively transmitted or shut off.
 4. Anoptical apparatus according to claim 3, wherein a surface of saidsee-through optical system on which outside world light is incident hasa configuration approximated to the first surface of said ocular opticalsystem, and a surface of said see-through optical system from whichoutside world light emanates has a configuration approximated to thesecond surface of said ocular optical system.
 5. An optical apparatusaccording to claim 1, further comprising: a see-through optical systemdisposed in the vicinity of the second surface of said ocular opticalsystem to transmit a bundle of light rays from an outside world and leadit to the second surface of said ocular optical system; and a shutterprovided at a side of said see-through optical system which is closer tothe outside world, said shutter allowing light to be selectivelytransmitted or shut off.
 6. An optical apparatus according to claim 5,wherein a surface of said see-through optical system on which outsideworld light is incident has a configuration approximated to the firstsurface of said ocular optical system, and a surface of said see-throughoptical system from which outside world light emanates has aconfiguration approximated to the second surface of said ocular opticalsystem.
 7. An optical apparatus comprising: a device for displaying animage; and an ocular optical system for projecting an image formed bysaid device and for leading the image to an observer's eyeball, saidocular optical system comprising at least first, second and thirdsurfaces, in which a space defined by said surfaces is filled with amedium, said device being disposed at a position facing said thirdsurface, said at least first, second and third surfaces including, inorder from the observer's eyeball side toward said device, said firstsurface which serves as both a refracting surface and an internallyreflecting surface, said second surface which serves as a reflectingsurface of positive power and which faces said first surface and isdecentered or tilted with respect to an observer's visual axis, and saidthird surface which serves as a refracting surface closest to saiddevice, wherein at least said first surface in said ocular opticalsystem is formed from a rotationally asymmetric curved surface so as tocorrect aberrations produced by a decentered surface having an opticalaction.
 8. An optical apparatus according to claim 7, a combination ofsaid device and said ocular optical system being provided for each ofobserver's left and right eyeballs so as to lead an image to each of theobserver's left and right eyeballs.
 9. An optical apparatus according toclaim 8, wherein internal reflection from said first surface is totalreflection.
 10. An optical apparatus according to claim 7, whereininternal reflection from said first surface is total reflection.
 11. Anoptical apparatus according to any one of claims 7 to 10, wherein anyone of said first, second and third surfaces is a decentered asphericalsurface.
 12. An optical apparatus according to claim 11, wherein any oneof said first, second and third surfaces is an anamorphic surface. 13.An optical apparatus comprising: an image display device; and an ocularoptical system for projecting an image formed by said image displaydevice and for leading the image to an observer's eyeball, said ocularoptical system including a decentered optical element comprising atleast first, second, and third surfaces, in which a space defined bysaid surfaces is filled with a medium, said surfaces including, fromsaid observer's eyeball side toward said image display device, saidfirst surface serving as both a refracting surface and a totallyreflecting surface, said second surface serving as a reflecting surfaceof positive power which faces said first surface and is decentered ortilted with respect to an observer's visual axis, and said third surfaceserving as a refracting surface closest to said image display device,said image display device being disposed at a position facing said thirdsurface, said ocular optical system further including at least oneoptical surface having refracting action, said decentered opticalelement and said at least one optical surface being disposed in anoptical path which extends from said image display device to saidobserver's eyeball, wherein at least said first surface in said ocularoptical system is formed from a rotationally asymmetric curved surfaceso as to correct aberrations produced by a decentered surface having anoptical action.
 14. An optical apparatus according to claim 13, acombination of said device and said ocular optical system being providedfor each of observer's left and right eyeballs so as to lead an image toeach of the observer's left and right eyeballs.
 15. An optical apparatusaccording to claim 14, wherein said at least one optical surface isdisposed between said observer's eyeball and the first surface of saiddecentered optical element.
 16. An optical apparatus according to claim14, wherein said at least one optical surface is disposed between thethird surface of said decentered optical element and said image displaydevice.
 17. An optical apparatus according to claim 14, wherein said atleast one optical surface is decentered with respect to said observer'svisual axis.
 18. An optical apparatus according to claim 13, whereinsaid at least one optical surface is disposed between said observer'seyeball and the first surface of said decentered optical element.
 19. Anoptical apparatus according to claim 13, wherein said at least oneoptical surface is disposed between the third surface of said decenteredoptical element and said image display device.
 20. An optical apparatusaccording to claim 13, wherein said at least one optical surface isdecentered with respect to said observer's visual axis.
 21. An opticalapparatus according to any one of claims 13 to 20, wherein said at leastone optical surface and said decentered optical element form an airlens.
 22. An optical apparatus according to any one of claims 7 to 10and 13 to 20, further comprising means for positioning both said deviceand said ocular optical system with respect to an observer's head. 23.An optical apparatus according to any one of claims 7 to 10 and 13 to20, further comprising means for supporting both said device and saidocular optical system with respect to an observer's head so that saidoptical apparatus can be fitted to said observer's head.
 24. An opticalapparatus according to any one of claims 7, 10, 13, and 18 to 20,further comprising means for supporting a pair of said opticalapparatuses at a predetermined distance.
 25. An optical apparatusaccording to any one of claims 8, 9, and 14 to 17, further comprisingmeans for supporting said combinations at a predetermined distance. 26.An optical apparatus according to any of one claims 7 to 10 and 13 to20, wherein said ocular optical system is used as an imaging opticalsystem.
 27. An optical apparatus according to any one of claims 1through 16, wherein said medium is acrylic resin or glass.
 28. Anoptical apparatus according to any one of claims 7 through 20, whereinsaid medium is acrylic resin or glass.
 29. An optical apparatusaccording to claim 11, wherein said medium is acrylic resin or glass.30. An optical apparatus according to claim 12, wherein said medium isacrylic resin or glass.
 31. An optical apparatus according to any ofclaims 13 through 30, wherein said medium is acrylic resin or glass. 32.An optical apparatus according to claim 21, wherein said medium isacrylic resin or glass.
 33. An optical apparatus according to claim 22,wherein said medium is acrylic resin or glass.
 34. An optical apparatusaccording to claim 23, wherein said medium is acrylic resin or glass.35. An optical apparatus according to claim 24, wherein said medium isacrylic resin or glass.
 36. An optical apparatus according to claim 25,wherein said medium is acrylic resin or glass.
 37. An optical apparatusaccording to claim 26, wherein said medium is acrylic resin or glass.38. An optical apparatus comprising: an image-forming member that formsan image to be observed, and an ocular optical system provided to leadsaid image to an eyeball of an observer, wherein said ocular opticalsystem includes, in order from an image side thereof, a third surfacethat forms an entrance surface, a first surface that forms both areflecting surface and an exit surface, and a second surface that formsa reflecting surface, said first, second and third surfaces beingintegrally formed to face each other across a medium, and wherein atleast one of said first, second and third surfaces is formed from arotationally asymmetric curved surface that corrects aberration producedby a decentered surface.
 39. An optical apparatus according to claim 38,further comprising: an optical member located between said image-formingmember and the eyeball of said observer, said optical member consistingof a material differing in dispersion from a material of said medium.40. An optical apparatus according to claim 39, further comprising: afitting member fitted to a head of said observer to retain saidimage-forming member, said ocular optical system and said optical memberbeing in front of said observer.
 41. An optical apparatus according toclaim 39 or 40, wherein said optical member is placed between the firstsurface of said ocular optical system and the eyeball of said observer.42. An optical apparatus according to claim 41, wherein said opticalmember comprises at least one optical surface having refracting action.43. An optical apparatus according to claim 39 or 40, wherein saidoptical member is located between the third surface of said ocularoptical system and an image display device.
 44. An optical apparatusaccording to claim 43, wherein said optical member comprises at leastone optical surface having refracting action.
 45. An optical apparatusaccording to claim 39 or 40, wherein reflection at the first surface ofsaid ocular optical system is total reflection.
 46. An optical apparatusaccording to claim 39 or 40, wherein the second surface of said ocularoptical system is a reflecting surface arranged to give a positive powerto a light beam by reflection.
 47. An optical apparatus according toclaim 39 or 40, wherein the first, second and third surfaces of saidocular optical system are each formed from a rotationally asymmetriccurved surface that corrects aberration due to decentration.
 48. In anoptical apparatus comprising an image-forming member that forms an imageto be observed, and an ocular optical system provided to lead said imageto an eyeball of an observer, the improvement wherein said ocularoptical system includes, in order from an image side thereof, a thirdsurface that forms an entrance surface, a first surface that forms botha reflecting surface and an exit surface, and a second surface thatforms a reflecting surface, said first, second, and third surfaces beingintegrally formed to face each other across a medium, at least one ofsaid first, second, and third surfaces is formed from a rotationallyasymmetric curved surface that corrects aberration produced by adecentered surface, and an optical member is placed between said ocularoptical system and the eyeball of said observer, said optical membertransmitting light exiting from said ocular optical system.
 49. Anoptical apparatus according to claim 48, further comprising: a fittingmember fitted to a head of said observer to retain said image-formingmember, said ocular optical system and said optical member in front ofsaid observer.
 50. An optical apparatus according to claim 48 or 49,wherein said optical member includes an entrance surface and an exitsurface, which face each other across a medium, said entrance surfacebeing placed on a side of said optical member closer to said ocularoptical system, said exit surface being placed on a side of said opticalmember closer to the eyeball of said observer.
 51. An optical apparatusaccording to claim 48 or 49, wherein reflection at the first surface ofsaid ocular optical system is total reflection.
 52. An optical apparatusaccording to claim 48 or 49, wherein the second surface of said ocularoptical system is a reflecting surface arranged to give a positive powerto a light beam by reflection.
 53. An optical apparatus according toclaim 48 or 49, wherein the first, second, and third surfaces of saidocular optical system are each formed from a rotationally asymmetriccurved surface that corrects aberration due to decentration.